The performance of chemical or biochemical analyses, assays, syntheses or preparations often requires a large number of separate manipulations to be performed on the material(s) or component(s) to be assayed, including measuring, aliquotting, transferring, diluting, mixing, separating, detecting, incubating, etc. Microfluidic technology miniaturizes these manipulations and integrates them so that they can be executed within one or a few microfluidic devices. For example, pioneering microfluidic methods of performing biological assays in microfluidic systems have been developed, such as those described by Parce et al., “High Throughput Screening Assay Systems in Microscale Fluidic Devices” U.S. Pat. No. 5,942,443 and Knapp et al., “Closed Loop Biochemical Analyzers” (WO 98/45481).
Many examples of microfluidic devices incorporate capillary or other similar elements extending from body structures of the devices. See, e.g., U.S. Pat. No. 6,149,787, issued Nov. 21, 2000, entitled “External Material Accession Systems and Methods,” to A. Chow et al., for an illustration of one possible microfluidic device incorporating capillary elements. Typically, a capillary element, which includes a capillary channel disposed therethrough, provides fluid communication between, e.g., a microchannel, microreservoir, microchannel network, or other similar cavity or element housed within the body structure of a microfluidic device and a fluid source outside of the microfluidic device. Such capillary elements are optionally used to load reagents, samples, or other materials from external sources, such as microwell plates, into the microfluidic device (or more specifically into desired microchannels, etc.).
Typically, as part of the preparation and/or manufacture of microfluidic devices, the microfluidic elements (e.g., microchannels, capillary elements, etc). are often filled and wetted with a desired gas, or more typically, a desired fluid, before the specific assays, etc. for which the microfluidic device was designed, are performed. One concern associated with the pre-filling of microfluidic devices containing capillary elements is the possibility of bubbles (of air or other gasses) being trapped within the junction or area where the capillary element joins/abuts the substrate layers of the microfluidic device. This is especially true with increasingly small junction areas. Bubbles can also be of concern in the pre-filling of microfluidic devices that have complex or intricate combinations of microfluidic elements (e.g., microchannels, etc.). For example, initial filling of microchannels containing large changes in cross-sectional area can present regions wherein bubbles (or other incomplete pre-filling problems) can be of concern.
A welcome addition to the art would be the ability to pre-fill microfluidic devices containing such capillary elements and complex/intricate microfluidic element configurations in microfluidic devices without the concern of bubbles being trapped in the interface between the capillary element and the substrate layer(s) of the microfluidic device or within the microfluidic elements of the device. The present invention includes methods and devices that accomplish these objectives.